An on-chip temperature sensing device is disclosed. The disclosed on-chip temperature sensing device is capable of sensing an environmental temperature of the chip. The device comprises a reference generating circuit, a first oscillator, a second oscillator, and an arithmetic logic unit. The reference generating circuit is configured to generate a first control voltage to control the first oscillator and the second oscillator. The bias current of the first oscillator and the bias current of the second oscillator are both controlled by the first control voltage so that the bias current of the first oscillator is directly proportional the bias current of the second oscillator regardless the environmental temperature. The first oscillator generates a first oscillation signal, while the second oscillator generates a second oscillation signal. The arithmetic logic unit may calculate the environmental temperature according to the first oscillation signal and the second oscillation signal.