In 1 MHz discharges of CF4/N2 mixtures at a total pressure of 0.5 Torr, the synergistic variation of the electron temperature was observed with various gas mixing ratios. This variation at CF4 ratio of around 95% is ascribed to the enhancement of electronegativity, and another at CF4 ratio of around 20% is due to the expansion of the discharge region outward from the space between electrodes.