- Analyses of heat spreading, temperature distribution, and resultant cooling effects in a monolithically Peltier‐cooled laser (MPCL) structure are presented. The analyses were obtained by using Laplace’s equation and were made under steady‐state conditions, assuming constant thermal conductivity. In this MPCL structure a metal surface layer surrounds a heat‐generating p‐n laser junction. It is shown that by depositing relatively thick metallic cooling plates a 15% temperature reduction and 25% thermal spreading can be achieved. This heat spreading due to the passive cooling is added to the cooling obtained when the Peltier cooler is operated. Experimental measurements of the effect of Peltier cooling reveal a 6.8 °C reduction in junction temperature corresponding to a wavelength shift of as much as 20 Å.