Testing of on-chip RF and microwave circuits has always been a challenge for test engineers. Since the emergence of Systems-on-a-Chip (SoCs), characterization and test development for SoCs has become a significant part of the RF IC manufacturing cost. In this paper, we propose a RF built-in-test methodology using on-chip sensors. Instead of measuring the device performance metrics (not possible for embedded RF circuits), the sensor output values (low frequency or DC) are used to estimate the performance metrics of the embedded device under test (DUT). The method has high coverage of defective DUTs for low-yielding processes. An algorithm for optimal placement of sensors on internal transceiver nodes is presented and two test cases are discussed. In this paper, we use the sensor outputs to obtain an estimate of the specification values of the system and the individual modules. Using this method, test specification values can be estimated with very high accuracy.