In this work, heat flux sensitivity of a large-integrated thermoelectric (TE) device has been experimentally investigated. The TE device was fabricated using a standard Si-CMOS technology, without needs for open cavity spaces commonly required in conventional TE devices. This architecture allows for both high detection sensitivity and minimal impact on the measurement target. This research presents a large-scale integrated TE device that utilizes 70668 stages of silicon nanowire (Si-NW) thermoelements and exhibits a prominent heat flux sensitivity of around 465 mV/W.