A 128-channel linear array photodetector, with 25 μm pixel pitch, connected to a readout integrated circuit (ROIC) was developed for mid-infrared spectroscopic applications that use a wavelength-variable quantum cascade laser (QCL). The detector is composed of III-V semiconductor InAsSb, has sensitivity in the mid-infrared region, and is operated at room temperature. The photovoltaic type of MIR detectors has a low shunt resistance, which causes high dark current. Therefore, a multiseries detector, which has a high total shunt resistance, is generally used for uncooled operation. However, in our newly developed detector array, a single element is employed as each channel's detector to achieve high signal sensitivity. Also, a DC feedback (DCFB) mechanism is applied to the ROIC to draw out the detector's high dark current. The detector's performance is evaluated using a pulsed QCL with an emission wavelength of 7-10 μm at room temperature. A reverse voltage is applied to the detector to improve the detector's characteristics and allow it to respond to a QCL's pulse width of 100 nsec. Although the reverse voltage increases the detector's dark current, the DC feedback draws out the dark current up to 1 mA. The detector's sensitivity is 1.5 A/W at 7 μm, the TIA's gain is designed to be 1k ohm, so the total trans gain obtained is 1.5 V/mW. The detector's noise input equivalent power is 200 nW. Therefore, a high signal-to-noise ratio can be achieved because the pulsed QCL can output a peak power higher than several tens of milliwatts.