Surface lattice resonance (SLR) lasers, where the gain is supplied by a thin-film active material and the feedback comes from multiple scattering by plasmonic nanoparticles, have shown both low threshold lasing and tunability of the angular and spectral emission at room temperature. However, typically used materials such as organic dyes and QD films suffer from photodegradation, which hampers practical applications. Here, we demonstrate photostable single-mode lasing of SLR modes sustained in an epitaxial solid-state InP slab waveguide. The nanoparticle array is weakly coupled to the optical modes, which decreases the scattering losses and hence the experimental lasing threshold is as low as 94.99 ± 0.82 μJ cm² pulse^-1. The nanoparticle periodicity defines the lasing wavelength and enables tunable emission wavelengths over a 70 nm spectral range. Combining plasmonic nanoparticles with an epitaxial solid-state gain medium paves the way for large-area on-chip integrated SLR lasers for applications, including optical communication, optical computing, sensing, and LiDAR.