David Tepper's Appaloosa Management is betting on T-Mobile, while cutting back on its investment in Southwest Airlines.

The hedge fund disclosed in a Wednesday filing a nearly 3.86 million-share stake in T-Mobile in the fourth quarter of last year. Appaloosa also reduced its holding in Southwest Airlines by nearly 700,000 shares, to 74,265 shares.

Both stocks are lower so far this year. T-Mobile is off 7.7 percent. Southwest shares are down 11.8 percent for 2018.

Appaloosa also increased its stake in Apple by 3.2 million shares to nearly 4.6 million shares and raised its holdings in Bank of America by 10.8 million shares to 17.15 million shares. The hedge fund bought about 10.45 million shares of semiconductor manufacturer Micron Technology to bring the total stake to 27.5 million shares.

The new positions were disclosed as part of a required quarterly filing with the U.S. Securities and Exchange Commission. The information is at least 45 days old and may not reflect the fund's current holdings.

Tepper said on CNBC's "Halftime Report" on Jan. 4 that the market "looks almost as cheap as [it was] coming into last year" given the tax cuts that President Donald Trump signed into law in December.

The gained 19 percent in 2017 but has struggled to hold this year's gains after suffering its first correction — a 10 percent drop — in two years.