The luminescent coupling (LC) effect is one of the strategies for further boosting the efficiency of multijunction solar cells by improving the current mismatch among subcells. This work examined the LC effect in III–V compound InGaP/GaAs/InGaAs inverted metamorphic triple-junction solar cell (IMM-3JSC) by the laser beam-induced current mapping characterization method. A strong LC effect in the bottom subcell of the IMM-3J sample was demonstrated with an LC yield of around 0.13 under 7 suns irradiance. In addition, by effectively homogenizing the LC effect, the bottom subcell of IMM-3JSCs may potentially gain a current density of ∼0.6 mA/cm2 at 10 suns irradiance.