VLBI observations of stellar masers provide important constraints on models for maser excitation and for the dynamics and physical conditions in circumstellar envelopes. The spatial distribution and apparent sizes of Si0 masers toward several late type variable stars and toward the star-forming region in Orion have been measured using the 75 km baseline between the 37 m telescope of Haystack Observatory and the 14 m telescope of the Five College Radio Astronomy Observatory. The fringe spacing is 0.02 arcsec and the transitions observed were the v = 1, J = 1 - 0 and v = 2, J = 1 - 0 lines at 43 GHz. The data were obtained in September 1979 and April 1982.