High energy Si implantation into GaAs is of interest for the fabrication of fully implanted monolithic microwave integrated circuits. 30Si has been implanted into LEC GaAs at energies of 1, 2, 4, and 6 MeV. We have measured atomic concentration profiles using SIMS and carrier concentration profiles using an electrolytic CV procedure. Theoretical atomic profiles have been calculated using TRIM-86. Excellent SIMS dynamic range and low background (<1014/cm3) was achieved for the profiles by the use of 30Si. The range statistics and profile shape factors: Rm, Rp, ΔRp, skewness (Y1), kurtosis (B2), and maximum Si density (Nmax) have been determined from the SIMS data by applying a Pearson IV computer fitting routine. The first two moments (Rp and ΔRp) were also obtained from the carrier profiles and the theoretical profiles. The range and standard deviation obtained from each profile have a maximum difference of only 15%, and the difference is usually less than 10%. This is less than the mutual experimental uncertainty of 17%. The samples were activated using a furnace anneal (800°C, 15 min) with a Si3N4 cap and using rapid thermal anneal (1000°C, 10s) with and without a Si3N4 cap. No redistribution of Si was observed for any of the anneal conditions within experimental error.