A thermocatalytic hydrogen (H₂) gas sensor based on pseudo-porous networks of cauliflower-like nanostructured Pt crystals (Pt black), as the catalytic material, has been fabricated through electrodeposition onto a strip-type suspended microheater (9 μm × 110 μm) for low power sensor operation (8 mW) and fast response speed (1.8 s). The electroplating parameters (solution concentration, current strength, and time) have been tuned for maximum sensitivity and an ionic solution of platinic acid with lead acetate has been used for high adhesion of the catalytic layer. The high catalytic activity of the Pt black, small size of the device, and highly localized electroplating method used allow for sensitive H₂ detection: ∼0.75% resistance change per %H₂ and an estimated 75-ppm lower limit of detection. Additionally, the sensor shows high selectivity against other flammable gases, while consuming much lower power than the commercial catalytic combustion based H₂ sensors. The low power consumption attained in this work is expected to help in the constant need for miniaturization of portable devices using catalytic gas sensor for selective detection in industry and for personalized applications.