This brief reports a class-C mode-switching single-ended-complementary (MS-SEC) VCO for wideband operation. Unlike the existing wideband VCOs that utilize nMOS-only $-\text{g}_{\text{m}}$ transistors operating in the class-B mode to maximize the oscillation amplitude, our MS-SEC VCO combines the advantages of class-C mode, which delivers a tall current pulse, together with current-reuse to maximize the current efficiency while lowering the phase noise (PN). The $-{g}_{m}$ transistors are preserved within the saturation region to avoid the inherent trade-off between PN and power consumption for a wideband VCO, as well as the reliability concerns. The VCO prototyped in 130-nm CMOS occupies a die area of 0.33 mm and consumes 5.1-to-7.3 mW at 1.2 V, while covering 2.4-to-5 GHz and meeting the stringent PN specification of the GSM standard with no SAW filter. The results correspond to a figure-of-merit of >190 dBc/Hz throughout the tuning range.