We present an analytical physical model for above-threshold leakage in semiconductor lasers. The model can be applied to estimate whether heterobarrier lowering and accompanying overbarrier leakage are within reach of having serious deleterious effects on laser performance. The model uses two-dimensional fully self-consistent numerical equations that arise from comprehensive systems of partial coupled differential equations. The effect of temperature and doping on laser efficiency is analyzed for two lasers, one designed for operation at 1.3 /spl mu/m and the other at 1.55 /spl mu/m. Both devices are assumed to be built in the InGaAsP-InP material system. We show that, even in a 1.55-/spl mu/m laser, overbarrier leakage can cause severe performance degradation at typical operating temperatures and doping levels, and we argue that overbarrier leakage deserves to be treated as a potential threat to laser performance at telecommunication wavelengths.