An anomalous dependence of the threshold current on the stripe width is observed for gain‐guided strained‐layer InGaAs/GaAs quantum well lasers. The threshold current increases strongly as the stripe width is reduced from relatively large values. This is attributed to the huge lateral loss caused by an unusually large index antiguide which manifests itself in the far‐field behavior. This large loss also leads to a population of higher quantized energy levels in the InGaAs quantum well strongly reducing the lasing wavelength by as much as 61 nm.