A temperature-compensated high-frequency CMOS integrated relaxation oscillator with low frequency variations is presented. A current-controlled oscillator topology is employed with a resistive source-degenerated transconductor and a current comparator to achieve high oscillation frequency and low power dissipation. The proposed oscillator was designed with process parameters from a standard 0.35- $$\upmu $$ μ m CMOS technology and a 2.5-V single power supply voltage. At a nominal oscillation frequency of 21 MHz, the total power dissipation of the circuit was 201 $$\upmu $$ μ W. Post-layout simulation results showed that the frequency variations were less than $${34.16\,\hbox {ppm}/{^{\circ }\hbox {C}}}$$ 34.16 ppm / ∘ C over a temperature range of $$-40$$ - 40 to $$+120\,^{\circ }\hbox {C}$$ + 120 ∘ C .