We present the concept and detailed design of a Smart Slit Assembly for next generation spectrometers, and we experimentally demonstrate operation of an individual 221 mu m x 111 mu m smart slit channel employing a MEMS actuated shutter to continuously modulate the intensity of the optical input signal. The MEMS actuated shutter is fabricated in a 211 mu m thick device layer of a Silicon-On-Insulator wafer by Deep Reactive Ion Etching. Electrostatic comb drive actuators allow an absolute displacement of 52 mu m at 74 V, resulting in a continuously tunable shutter efficiency of up to 99.97% at an operating wavelength of 532 nm.