The spatial mode characteristics of gain‐guided broad‐area quantum well lasers grown by organometallic chemical vapor deposition were investigated experimentally. GaAs/AlGaAs quantum well lasers grown on 6°‐off (100) oriented substrates exhibit excellent material uniformity, which allows study of their modal behavior. Gain‐guided broad‐area lasers fabricated on such uniform material demonstrate nearly ideal gain‐guiding modal behavior. These lasers tend to lase in the fundamental mode near threshold and emit single‐lobed far‐field patterns. In these well‐behaved broad‐area lasers, we have identified the mechanism for degradation in the spatial coherence at high pumping levels as the onset of higher order lateral modes.