Developing semiconductors with broad gain bandwidth has always been at the forefront of laser technologies. The variation in feedback resonators can provide a useful tool for producing a relatively wide range of discrete lasing wavelengths. However, the lasing wavelength range is limited by the fundamental gain bandwidth of the semiconductor itself. Gain bandwidth engineering for full-color range lasing though remains a daunting challenge. Considering the abundant energy levels of organic semiconductors, the authors stride over the barrier of the gain bandwidth limitation and demonstrate the dynamically tunable amplification/lasing across the entire emission range by leveraging on Förster resonance energy transfer (FRET)-assisted guest–host blends. The unprecedented tunability in amplification and lasing is governed by energy transfer process, which enables them to achieve wavelength-tunable semiconductor lasers spanning the full visible region of the electromagnetic spectrum. Their distributed feedback (DFB) lasers using these guest–host blends as gain media cover almost all CIE color gamut (94%), which is 170% more perceptible colors than standard Red Green Blue color space. These insights can guide the versatile and convenient design of organic semiconductor materials transcending the current gain bandwidth limitation, paving the way for next generation of optoelectronic devices.