This paper presents the performance of a highly selective ethanol sensor based on MoS2-functionalized porous silicon (PSi). The uniqueness of the sensor includes its method of fabrication, wafer scalability, affinity for ethanol, and high sensitivity. MoS2 nanoflakes (NFs) were synthesized by sulfurization of oxidized radio-frequency (RF)-sputtered Mo thin films. The MoS2 NFs synthesis technique is superior in comparison to other methods, because it is chip-scalable and low in cost. Interdigitated electrodes (IDEs) were used to record resistive measurements from MoS2/PSi sensors in the presence of volatile organic compound (VOC) and moisture at room temperature. With the effect of MoS2 on PSi, an enhancement in sensitivity and a selective response for ethanol were observed, with a minimum detection limit of 1 ppm. The ethanol sensitivity was found to increase by a factor of 5, in comparison to the single-layer counterpart levels. This impressive response is explained on the basis of an analytical resistive model, the band gap of MoS2/PSi/Si, the interface formed between MoS2 and PSi, and the chemical interaction of the vapor molecules and the surface. This two-dimensional (2D) composite material with PSi paves the way for efficient, highly responsive, and stable sensors. © 2017 American Chemical Society.