William Harnisch Peconic Partners
William Harnisch is the founder of Peconic Partners, a concentrated investment firm known for high-conviction equity positions. The firm’s portfolio often differs sharply from broad market benchmarks, reflecting a willingness to concentrate capital. Harnisch’s disclosures are tracked by investors interested in bold, research-driven concentration.
Top Buys
| Rank | Stock | Value |
|---|---|---|
| 1 |
MasTec
MTZ
|
+$137M |
| 2 |
Dycom Industries
DY
|
+$78.6M |
| 3 |
Warner Bros
WBD
|
+$13.6M |
| 4 |
AMC Entertainment Holdings
AMC
|
+$5.94M |
| 5 |
EQT Corp
EQT
|
+$5.28M |
Top Sells
| Rank | Stock | Value |
|---|---|---|
| 1 |
State Street Utilities Select Sector SPDR ETF
XLU
|
+$81.7M |
| 2 |
First Solar
FSLR
|
+$38.4M |
| 3 |
Alphabet (Google) Class A
GOOGL
|
+$37.3M |
| 4 |
Amazon
AMZN
|
+$29.4M |
| 5 |
Array Technologies
ARRY
|
+$2.2M |
Sector Composition
| Rank | Sector | Weight |
|---|---|---|
| 1 | Industrials | 95.02% |
| 2 | Technology | 2.54% |
| 3 | Energy | 1.71% |
| 4 | Communication Services | 0.71% |
| 5 | Consumer Discretionary | 0.02% |
| Name | Market Value | Portfolio Weight | Shares or Principal |
Change in Stake | Capital Flow | |
|---|---|---|---|---|---|---|
1
Quanta Services
PWR
$96.1B
| $2.08B | 57.39% |
5,007,840
+11,191
| +0.2% | +$4.35M |
|
|
2
Dycom Industries
DY
$11.8B
| $1.2B | 33.22% |
4,117,320
+299,495
| +8% | +$78.6M |
|
|
3
MasTec
MTZ
$21.4B
| $160M | 4.41% |
+750,000
| New | +$137M |
|
4
Shoals Technologies Group
SHLS
$1.19B
| $52.3M | 1.45% |
7,054,803
+79,617
| +1% | +$490K |
|
|
5
EQT Corp
EQT
$33.6B
| $31.6M | 0.87% |
580,000
+100,000
| +21% | +$5.28M |
|
6
Range Resources
RRC
$9.59B
| $30.1M | 0.83% |
800,000
| – | – |
|
|
7
First Solar
FSLR
$23B
| $22.1M | 0.61% |
100,000
-200,000
| -67% | -$38.4M |
|
|
8
Warner Bros
WBD
$71.6B
| $19.5M | 0.54% |
+1,000,000
| New | +$13.6M |
|
|
9
Array Technologies
ARRY
$722M
| $17.4M | 0.48% |
2,130,783
-290,000
| -12% | -$2.2M |
|
|
10
AMC Entertainment Holdings
AMC
$2.28B
| $5.8M | 0.16% |
+2,000,000
| New | +$5.94M |
|
|
11
Amazon
AMZN
$2.79T
| $874K | 0.02% |
3,980
-130,000
| -97% | -$29.4M |
|
|
12
Alphabet (Google) Class A
GOOGL
$4.22T
| $438K | 0.01% |
1,800
-178,200
| -99% | -$37.3M |
|
13
Nextpower Inc
NXT
$13.1B
| – | – |
-10,000
| Closed | -$544K |
|
|
14
State Street Utilities Select Sector SPDR ETF
XLU
$22.2B
| – | – |
-2,000,000
| Closed | -$81.7M |
|
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William Harnisch's Q3 2025 Portfolio in Review
As of Q3 2025, William Harnisch held 14 positions worth $3.62B, up 16% from $3.12B the previous quarter. Its ten largest holdings account for 100% of the portfolio.
William Harnisch's Q3 2025 filing shows 3 new, 4 increased, 4 reduced and 2 closed positions. Its largest new stake was MasTec: 750,000 shares worth $160M. The largest sale was State Street Utilities Select Sector SPDR ETF, an estimated $81.7M.
By sector, the portfolio is most concentrated in Industrials at 95% of assets, up from 90% a quarter earlier, followed by Technology and Energy.
- William Harnisch's largest Q3 2025 buy was MasTec: 750,000 shares worth $160M.
- William Harnisch added most to Dycom Industries in Q3 2025, an estimated $78.6M increase.
- William Harnisch's biggest Q3 2025 reduction was First Solar, cutting an estimated $38.4M.
- William Harnisch fully exited State Street Utilities Select Sector SPDR ETF in Q3 2025, selling an estimated $81.7M.
- William Harnisch's ten largest holdings make up 100% of its $3.62B portfolio in Q3 2025.
- William Harnisch opened 3 new positions and closed 2 in Q3 2025.
- William Harnisch's portfolio value rose 16% quarter-over-quarter to $3.62B.
Based on Peconic Partners's 13F filing for Q3 2025, filed 14 Nov 2025.