Federal Communications Com­mission Chairman Julius Genachowski will announce Friday that he is stepping down, according to an FCC official, leaving the agency after a four-year term that focused heavily on improving Internet access across the country.

Genachowski told FCC staff members on Thursday of his plans to make the Friday announcement, the official and an industry source said. Genachowski, a Democrat, has been widely expected to exit in coming weeks. His term expires in June.

A spokesman in Genachow­ski’s office declined to comment.

The news comes in the same week that Robert McDowell, the senior Republican among the five commissioners, said he would leave in a few weeks. The departures will leave Mignon Clyburn and Jessica Rosenworcel as the FCC’s Democrats and Ajit Pai as its sole Republican. The FCC oversees the TV, radio, cable, satellite and Internet industries.

Rules governing FCC appointments mean President Obama must nominate a new Republican commissioner and a Democratic chairman. The two are likely to go through Senate confirmation at the same hearing.