  By studying the Hall effect in a series of low resistivity Ga1-xMnxAs
samples, accurate values for the hole density p, Mn concentration x, and Curie
temperature Tc are obtained over the range 0.015=<x=<0.08. The hole density
corresponds to 90% of the Mn concentration at low x, and has a maximum value of
1.0x10-27 m-3 when Tc=125K for x=0.06. This data allows the first meaningful
comparison of mean field predicted Curie temperatures with experiment over a
wide range of x. The theory is in qualitative agreement with experiment, but
overestimates Tc at large x and underestimates TC at low x.
