This paper describes experimental study about cooling performance of natural and forced air convection in compact heat sinks for LSI packages. Temperature rise of several heat sinks having different base areas, fin intervals and fin heights was measured. In natural convection case, the effect of supplied power on the temperature rise of the fin was examined. In forced convection case, correlations between air flow velocity and temperature rise were examined. Further, based on those results, non-dimensional expressions to evaluate cooling performance of compact heat sinks were proposed.