The strong piezoelectric effect and quantum confined stark effect (QCSE) in the InGaN/GaN quantum well structures allow one to modify the free exciton absorption by the extrinsic field. The QCSE is investigated using a monolithically integrated three-section device comprising an LED, electroabsorption modulator and a detector section. The experimental results show that the LED output can be modulated as indicated by the detector signal. The strength of modulation decreases monotonically with increasing In composition in the InGaN/GaN MQW. The result can be explained on the basis of the Stokes' shift between the emission and absorption spectra in the InGaN/GaN QW structure, and a blue shift of the absorption spectrum due to the QCSE as a result of the piezoelectric effect.