X-ray powder diffraction measurements on MnGa2Se4, a II-III2-VI4 semimagnetic semiconductor compound, are made in the temperature range between 300 and 700 K, a region in which this material has a defect tetragonal structure. From the analysis of the X-ray diffraction lines, accurate lattice parameter values are determined as a function of temperature. These results allow the evaluation of the thermal expansion coefficients of the corresponding parameters. The observed increases of the tetragonal deformation δ ( = 2 - c/a) as well as of the crystal anisotropy Aa ( = αa - αc, with αa > αc) with temperature are explained by using the relations proposed by Abrahams and Bernstein.