The Radio-Frequency Identification (RFID) is an automatic identification method using RF waves to transfer data between reader units and moveable objects called a transponder or a tag [1-5]. The DC power required for the operation of a RFID tag is obtained from the surrounding RF signal by a power harvester and the energy is then stored in a capacitor. One way to manage the charge of the capacitor is to directly utilize the energy stored in the capacitor as the supply for the rest of the circuits. However, in this case, the supply of the system may be interrupted by short absences of the RF signal and this limits the operating range of the system. To tackle this problem, a voltage sensor is introduced for sensing the stored voltage in the capacitor and powering up the entire system and its usage is recommended by the EPC RFID Gen2 protocol [6]. Some voltage sensor architectures are proposed [7-9]. However, all of them suffer from some deficiencies such as large variation with respect to corner process. In this paper, a novel process-invariant voltage sensor architecture with flexible threshold voltage controllability is proposed, designed and simulated with a 0.18 μm CMOS technology from XFAB. Besides this introductory section, there are additional three sections in this paper. The proposed voltage sensor architecture and its sub-blocks are described in Section II. In Section III, simulation results of the proposed voltage sensor are presented. Finally, the conclusion will be drawn in Section IV.