Polycrystalline CuInSe2 (CIS) and Cu(In,Ga)Se-2 (CIGS) thin-films were grown by co-evaporation on a soda lime glass substrate. Rapid thermal processing (RTP) in H2S atmosphere with processing temperatures ranging from 350 to 550 degreesC was used to sulfurize the absorber. The change in microstructure after sulfurization and annealing was characterized mainly by transmission electron microscopy. A non-uniform and porous surface reaction layer is evident in the CIS and CIGS structures after the RTP. The CIGS structure have a tendency towards a phase separation, whereas, the CIS films exhibit mixed sulfoselenides, CuIn(Se1-xSx)(2), where x varies. In order to improve the device performance, the formation of two distinct phases should be avoided during the sulfurization processing.