  The critical behavior of Ga1-xMnxAs in a close vicinity of the Curie
temperature was experimentally studied by using the thermal diffusivity
measurements. Taking into account that the inverse of the thermal diffusivity
has the same critical behavior as the specific heat, the critical exponent
{\alpha} for the samples investigated has been determined. With approaching
close to the critical temperature, the crossover from the mean-field-like to
the Ising-like critical behavior has been observed. From the crossover behavior
the values of the Ginzburg number and the exchange interaction length in
Ga1-xMnxAs with different concentrations of Mn were determined.
