Monolithically integrated master oscillator power amplifiers (M-MOPA’s) have been characterized both theoretically and experimentally. a self-consistent amplifier analysis is used to calculate the guided-mode amplified signal and amplified spontaneous emission noise powers traveling within a multiple-stage single-pass amplifier. Within a few amplifier stages, the signal power stabilizes at a level determined by the transmission between stages. Light output versus current and near-field and far-field patterns are calculated for an M-MOPA with detuned grating output couplers between stages, and are compared to experiments. Coherent output powers in excess of 1 W are calculated and experimentally verified. in addition, diffraction-limited performance has been demonstrated to output powers of320 mW.