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Main Street Research LLC — 13F Holdings & Portfolio

CIK 1513211 · latest 13F-HR filed 2026-07-29

Backtest portfolio

Main Street Research LLC manages $2.12B in 13F-reported U.S. long-equity assets across 140 reported positions as of its 2026-06-30 13F-HR filing. Its largest disclosed positions are NVDA (5.95%), MU (5.92%), AAPL (5.55%). Quarter over quarter (versus its 2026-03-31 filing) the fund opened 13 new positions and exited 21; 80 existing positions rose in reported value and 27 fell.

AUM is the long-equity portion reported on Form 13F-HR. Excludes short positions, cash, foreign holdings, and non-13F assets. For informational purposes only — not investment advice.

Loading holdings…
AUM
$2.12B

Long-equity book

Holdings
140

Distinct positions

Period
2026-06-30

Filed 2026-07-29

Q/Q Activity
+13 / −21 / ↑80 / ↓27

vs 2026-03-31

Portfolio charts

Latest quarter's book, what changed, and how the portfolio has evolved across filings.

Portfolio map

Q2 26
NVDA6.0% · +2%MU5.9% · -0%AAPL5.5% · +1%GOOGL5.3% · +2%TSM5.1% · +2%GLW4.8% · +2%XBI4.3% · +2%ISCF4.1% · +4%ASML4.0% · +2%AVGO3.8% · +1%JPM3.5% · +1%EWY3.4% · -0%CAT3.1% · +1%AMZN3.1% · +2%GEV2.8% · +0%APH2.6% · +2%JNJ2.3% · +1%RY2.2% · +2%COST2.1% · +3%BHP2.1% · +2%BCS2.1% · +90%META1.9% · +2%KEYS1.9% · +2%CCJ1.9% · +1%WMT1.9% · +1%AZN1.8% · +4%ROST1.5% · newFTI1.3% · newMSFT1.2% · +2%PG1.0% · -0%MCK1.0% · -58%FICO0.5% · +13%GOOG0.4% · -3%PANW0.4% · -31%BRK.B0.3% · 0%ANET0.3% · -0%TSLA0.3% · +5%SCHW0.2% · -1%WFC0.2% · +4%BRK.A0.2% · 0%IXUS0.2% · +1%LLY0.2% · -6%V0.2% · -9%XOM0.1% · -6%ADSK0.1% · -1%URTH0.1% · -8%CVX0.1% · -5%SPY0.1% · +7%ABBV0.1% · -5%MCD0.1% · -42%AMD0.1% · +5%IVV0.1% · -29%PLTR0.1% · -93%MMM0.1% · -3%ISTB0.1% · +2%CSCO0.1% · -4%QQQ0.1% · -14%RTX0.1% · -5%MRK0.1% · -13%TXN0.1% · +1%

Box size = position value; colour = change in share count vs the prior quarter (green added, red trimmed, blue new). Rows split across managers or share classes are combined. Click a box for the stock.

Sector mix

% of 13F value

Sectors from each company's SIC code; funds and ETFs grouped separately.

Biggest buys and sells

Q1 26 → Q2 26

Estimated from the change in shares held × the quarter-end price, so price moves alone don't count as buying. New and exited positions are included.

13F assets and positions

3 quarters

Total reported 13F value (bars) and number of positions (line) each quarter. Value changes include market moves.

Top positions over time

reported value

The eight largest current positions, valued at each quarter end.

Concentration

top 10 = 48.9%

Cumulative share of the portfolio held in the largest N positions.

Firm Profile & Key People

As of the firm’s regulatory filing dated Apr 27, 2026.

Assets Under Management
$2.68B
Discretionary
$2.68B
Employees
24
Accounts
3,017
Address
342 MAIN STREET
LAKEVILLE, CT 06039
Phone
(860) 435-2350
Website
Mailing Address
30 LIBERTY SHIP WAY THIRD FLOOR, SAUSALITO, CA, 94965
Name Title / Status Ownership Type
ARMELLINI, BENJAMIN, B ControlPARTNER - CHIEF EXECUTIVE OFFICER
since Apr 2026
5–10%Individual
DEMMERT, JAMES, EDMUND ControlMANAGING PARTNER AND CHIEF INVESTMENT OFFICER
since Apr 2000
75% or moreIndividual
McMahon, Natalie, Elaine ControlMANAGING PARTNER
since Apr 2026
Less than 5%Individual
McMahon, Natalie, Elaine ControlCHIEF COMPLIANCE OFFICER
since Feb 2024
Less than 5%Individual
STERN, AARON, MICHAEL ControlMANAGING PARTNER AND PORTFOLIO MANAGER
since Aug 2020
5–10%Individual
TAFT, LILY, NICOLE ControlMANAGING PARTNER
since Apr 2026
Less than 5%Individual
Ownership & leadership changes · 9 filings with changes since Nov 21, 2011

From the firm’s regulatory filings, newest first. Dates are filing dates: a filing that no longer lists someone does not say when they left.

Apr 27, 2026 filing
  • ChangedARMELLINI, BENJAMIN, B · title MANAGING PARTNER- EAST, PORTFOLIO MANAGER → PARTNER - CHIEF EXECUTIVE OFFICER; now a control person
  • ChangedMcMahon, Natalie, Elaine · title CHIEF COMPLIANCE OFFICER / PARTNER AND CHIEF OPERATING OFFICER → CHIEF COMPLIANCE OFFICER / MANAGING PARTNER
  • ChangedSTERN, AARON, MICHAEL · title MANAGING PARTNER -WEST, PORTFOLIO MANAGER → MANAGING PARTNER AND PORTFOLIO MANAGER
  • ChangedTAFT, LILY, NICOLE · title CHIEF STRATEGY OFFICER → MANAGING PARTNER
Mar 31, 2026 filing
  • AddedTAFT, LILY, NICOLE · CHIEF STRATEGY OFFICER · Less than 5% · control person
  • ChangedARMELLINI, BENJAMIN, B · ownership Less than 5% → 5–10%
Feb 2, 2024 filing
  • No longer listedPOMBRA, MANOJ, KUMAR · CHIEF COMPLIANCE OFFICER · Less than 5% · listed since Aug 2020
  • ChangedARMELLINI, BENJAMIN, B · title PARTNER, PORTFOLIO MANAGER → MANAGING PARTNER- EAST, PORTFOLIO MANAGER
  • ChangedMcMahon, Natalie, Elaine · title PARTNER AND CHIEF OPERATING OFFICER → CHIEF COMPLIANCE OFFICER / PARTNER AND CHIEF OPERATING OFFICER
  • ChangedSTERN, AARON, MICHAEL · title PARTNER - PORTFOLIO MANAGER → MANAGING PARTNER -WEST, PORTFOLIO MANAGER; ownership Less than 5% → 5–10%; now a control person
Mar 29, 2023 filing
  • ChangedDEMMERT, JAMES, EDMUND · title MANAGING PARTNER → MANAGING PARTNER AND CHIEF INVESTMENT OFFICER
  • ChangedMcMahon, Natalie, Elaine · title CHIEF OPERATING OFFICER → PARTNER AND CHIEF OPERATING OFFICER
  • ChangedSTERN, AARON, MICHAEL · title PARTNER - LEAD TRADER, PORTFOLIO MANAGER → PARTNER - PORTFOLIO MANAGER
Mar 30, 2022 filing
  • AddedMcMahon, Natalie, Elaine · CHIEF OPERATING OFFICER · Less than 5% · control person
Sep 4, 2020 filing
  • No longer listedSTERN, TAMRA, ANN · CHIEF COMPLIANCE OFFICER · Less than 5% · control person · listed since Mar 2004
  • AddedARMELLINI, BENJAMIN, B · PARTNER, PORTFOLIO MANAGER · Less than 5%
  • AddedPOMBRA, MANOJ, KUMAR · CHIEF COMPLIANCE OFFICER · Less than 5%
  • AddedSTERN, AARON, MICHAEL · PARTNER - LEAD TRADER, PORTFOLIO MANAGER · Less than 5%
Aug 25, 2020 filing
  • No longer listedMITTELMAN, CHARITO, ARROYO · CHIEF COMPLIANCE OFFICER, GENERAL COUNSEL · Less than 5% · listed since Feb 2011
  • ChangedSTERN, TAMRA, ANN · title PARTNER, DIRECTOR - WEALTH MANAGEMENT → CHIEF COMPLIANCE OFFICER
Mar 29, 2016 filing
  • AddedSTERN, TAMRA, ANN · PARTNER, DIRECTOR - WEALTH MANAGEMENT · Less than 5% · control person
Mar 27, 2015 filing
  • ChangedMITTELMAN, CHARITO, ARROYO · title CHIEF COMPLIANCE OFFICER → CHIEF COMPLIANCE OFFICER, GENERAL COUNSEL
Nov 21, 2011 filing (earliest on record)
  • ListedDEMMERT, JAMES, EDMUND · MANAGING PARTNER · 75% or more · control person
  • ListedMITTELMAN, CHARITO, ARROYO · CHIEF COMPLIANCE OFFICER · Less than 5%

Quarter-over-quarter changes

Changes in reported position value vs the prior 13F, so price moves count too, not just shares bought or sold.

Top Adds (vs prior quarter)

Show all 80 →

Top Trims

Show all 27 →

New Positions

Show all 13 →

Exited Positions

Show all 21 →

Main Street Research LLC Holdings (2026-06-30)

Rows tagged Call or Put are options positions, not stock. Per SEC Form 13F-HR, Value shows the notional value of the underlying (shares covered × underlying price), not the option premium. Shares is the number of underlying shares covered (divide by 100 for contract count).

# Issuer Symbol CUSIP Value Weight Shares Type
1 NVIDIA CORPORATION NVDA 67066G104 $126.1M 5.95% 630,053 SH
2 MICRON TECHNOLOGY INC MU 595112103 $125.4M 5.92% 108,636 SH
3 APPLE INC AAPL 037833100 $117.5M 5.55% 406,129 SH
4 ALPHABET INC GOOGL 02079K305 $113.3M 5.35% 316,947 SH
5 TAIWAN SEMICONDUCTOR MANUFAC TSM 874039100 $109.1M 5.15% 228,429 SH
6 CORNING INC GLW 219350105 $100.7M 4.75% 394,058 SH
7 SPDR SERIES TRUST XBI 78464A870 $91.3M 4.31% 576,754 SH
8 ISHARES TR ISCF 46434V266 $87.8M 4.14% 2,027,356 SH
9 ASML HLDG NV ASML N07059210 $84.3M 3.98% 42,396 SH
10 BROADCOM INC AVGO 11135F101 $80.8M 3.81% 213,841 SH
11 JPMORGAN CHASE & CO JPM 46625H100 $74.1M 3.50% 226,299 SH
12 ISHARES INC EWY 464286772 $72.9M 3.44% 360,865 SH
13 CATERPILLAR INC CAT 149123101 $65.8M 3.10% 61,759 SH
14 AMAZON COM INC AMZN 023135106 $65.5M 3.09% 274,738 SH
15 GE VERNOVA INC GEV 36828A101 $59.7M 2.82% 50,802 SH
16 AMPHENOL CORP APH 032095101 $54.4M 2.57% 308,716 SH
17 JOHNSON & JOHNSON JNJ 478160104 $47.9M 2.26% 188,640 SH
18 ROYAL BK CDA RY 780087102 $47.0M 2.22% 227,136 SH
19 COSTCO WHOLESALE CORPORATION COST 22160K105 $44.4M 2.10% 47,497 SH
20 BHP BILLITON LIMITED BHP 088606108 $44.0M 2.08% 528,051 SH
21 BARCLAYS PLC BCS 06738E204 $43.6M 2.06% 1,621,490 SH
22 META PLATFORMS INC META 30303M102 $40.7M 1.92% 72,187 SH
23 KEYSIGHT TECHNOLOGIES INC KEYS 49338L103 $40.3M 1.90% 115,108 SH
24 CAMECO CORP CCJ 13321L108 $39.9M 1.88% 391,529 SH
25 WALMART INC WMT 931142103 $39.5M 1.86% 348,650 SH
26 ASTRAZENECA PLC AZN G0593M107 $37.4M 1.77% 197,417 SH
27 ROSS STORES INC ROST 778296103 $32.1M 1.51% 150,755 SH
28 TECHNIPFMC PLC FTI G87110105 $27.4M 1.29% 413,657 SH
29 MICROSOFT CORP MSFT 594918104 $25.8M 1.22% 69,182 SH
30 PROCTER & GAMBLE CO PG 742718109 $22.2M 1.05% 151,073 SH
31 MCKESSON CORP MCK 58155Q103 $21.5M 1.02% 28,475 SH
32 FAIR ISAAC CORP FICO 303250104 $11.4M 0.54% 9,580 SH
33 ALPHABET INC GOOG 02079K107 $8.0M 0.38% 22,707 SH
34 PALO ALTO NETWORKS INC PANW 697435105 $8.0M 0.38% 23,343 SH
35 BERKSHIRE HATHAWAY INC DEL BRK.B 084670702 $6.0M 0.28% 11,980 SH
36 ARISTA NETWORKS INC ANET 040413205 $5.9M 0.28% 34,937 SH
37 TESLA INC TSLA 88160R101 $5.4M 0.26% 12,943 SH
38 SCHWAB CHARLES CORP SCHW 808513105 $4.2M 0.20% 45,887 SH
39 WELLS FARGO & CO WFC 949746101 $4.0M 0.19% 48,542 SH
40 BERKSHIRE HATHAWAY INC DEL BRK.A 084670108 $3.7M 0.18% 5 SH
41 ISHARES TR IXUS 46432F834 $3.7M 0.18% 39,073 SH
42 ELI LILLY & CO LLY 532457108 $3.3M 0.16% 2,746 SH
43 VISA INC V 92826C839 $3.2M 0.15% 9,369 SH
44 EXXON MOBIL CORP XOM 30231G102 $3.1M 0.14% 22,437 SH
45 AUTODESK INC ADSK 052769106 $2.8M 0.13% 14,240 SH
46 ISHARES INC URTH 464286392 $2.7M 0.13% 13,511 SH
47 CHEVRON CORPORATION CVX 166764100 $2.7M 0.13% 16,080 SH
48 STATE STR SPDR S&P 500 ETF T SPY 78462F103 $2.6M 0.12% 3,485 SH
49 ABBVIE INC ABBV 00287Y109 $2.4M 0.12% 9,721 SH
50 MCDONALDS CORP MCD 580135101 $2.4M 0.11% 8,913 SH
Filing History
Period Filed AUM Holdings Accession
2026-06-30 2026-07-29 $2.12B 140 0001420506-26-001335
2026-03-31 2026-04-30 $1.72B 148 0001420506-26-000773
2025-12-31 2026-02-09 $1.75B 129 0001420506-26-000210
Filer Information
Address
342 MAIN STREET
LAKEVILLE, CT 06039
Phone
(860) 435-2350
Filing Manager
Main Street Research LLC
SAUSALITO, CA
Signatory
Natalie McMahon
Chief Compliance Officer