We present a fast algorithm for calculations of the temperature distributions induced by the energy beam in the three‐dimensional deposits of arbitrary shape. It combines analytical approximations, numerical fast Fourier transform, and the multigrid technique. The accuracy of the method is demonstrated with problems that can be solved analytically. The behavior of the center temperature in laser‐deposited spots and stripes of different shapes and sizes is studied. The results can explain explosive growth in laser‐induced deposition and instabilities in laser direct writing, and provide a tool for a quantitative analysis of energy beam microprocessing. ©1996 American Institute of Physics.