A fully-integrated relaxation oscillator with a typical frequency of 1.37 MHz is proposed. Neither comparators nor the reference voltage is required in the proposed oscillator. A constant with temperature (CWT) current source has been utilized to achieve good temperature stability. Moreover, a conventional comparator has been replaced with a voltage controlled delay element (VCDE) to avoid the comparator offset effect. Fur­thermore, frequency variation against supply voltage has been eliminated by matching bias voltages of the current starved delay element (CSDE) in the ramp generator and VCDE. The proposed relaxation oscillator is implemented with 0.25 μm BCD process. The measured results show that the frequency variation against supply voltage is within ±0.6%.