A multi semiconductor source tunable spectroscopy system has two or more semiconductor sources for generating tunable optical signals that are tunable over different spectral bands. The system enables the combination of these tunable signals to form an output signal that is tunable over a combined band including these individual spectral bands of the separate semiconductor sources. The system further compensates for spectral roll-off associated with the semiconductor sources. Specifically, near the limits of the semiconductor sources' spectral bands, the power in the tunable signal tends to degrade or decrease. The system compensates for this roll-off using drive current control, attenuators, or electronic compensation.