Laser amplifiers when pumped to a significant degree of population inversion undergo decay via (1) natural spontaneous emission of radiation from individual excited atoms, and (2) a size‐dependent decay due to self‐amplification of the spontaneously emitted radiation which passes through a large fraction of the amplifier length before escaping. This latter effect has a definite size threshold near which the decay rate changes several orders of magnitude. The decay rate is roughly independent of size except near the threshold.