With any new drug many impacts are unknown.

If you search for “sofosbuvir semen” on Google you will only find 2 results.

Sofosbuvir was previously known as PSI-7977 and GSI-7977 so you should also search for

pharmasset psi-7977 semen

gilead gsi-7977 semen

The last search yields this result: http://www.natap.org/2014/EASL/nejmoa1316366_protocol.pdf however the excretion in semen refers to Ribavirin.

Anyway in the absence of documentation saying it’s not in semen you would be safest to refrain from trying to have children during treatment. The logic for how long to wait after treatment see:

http://fixhepc.com/forum/experts-corner/872-how-long-should-i-wait-after-treatment-before-getting-pregnant.html