This paper reports the first on-chip demonstration of GHz range real time spectrum analysis (RTSA) using an integrated dispersive delay line (IDDL). The IDDL is implemented in a standard 0.13 µm CMOS process and can operate from 0.4 GHz to 4 GHz with 1.2 ns dispersion. The IDDL provides a frequency-to-time mapping which can be utilized to generate a time domain representation of the frequency components. We demonstrate that the IDDL is capable of real time spectrum analysis of signals within the frequency range of 0.4 GHz to 4 GHz.