A new technique to crystallize as-deposited, amorphous phase in (BiDy) 3(FeGa)5O12 films is presented. This technique employs heat pulse annealing and leads to improved surface smoothness and smaller grains, in comparison with conventional oven anneal and also with in situ crystallization during deposition. Rapid thermal annealing was accomplished in a heat pulse apparatus with a ramp-up rate up to 50°C/s. Upon heating for several seconds at about 650°C, a single phase of garnet is formed. The samples were polycrystalline, but exhibit a perpendicular magnetic anisotropy of 104 erg/cm3, and a high squareness of Faraday hysteresis loops. The coercivity is typically 1-4 kOe. A systematic study of the effect of a ramp rate on a microstructure and magnetic properties has been made. The result indicates that the ramp-up rate is a key to controlling grain size and surface morphology.