Semantic annotation is an important part of corpus linguistics. A major tool for semantic tagger is the USAS developed at Lancaster University, which was originally designed for English but has been extended to cover many more languages. In the CorCenCC Project (http://sites.cardiff.ac.uk/corcencc), we are extending the USAS to automatically annotate Welsh language data with the USAS semantic tagset. In this paper, we report on the development of Welsh semantic lexicons for the semantic tagger, in which we have already built a Welsh semantic lexicon containing 143,290 entries that has achieved a lexical coverage of 72.42% in an initial evaluation. An initial version of the Welsh semantic tagger has already been developed based on the lexical resource.