In this letter, the AC performance and influence of bending on flexible IGZO thin-film transistors, exhibiting a maximum oscillation frequency (maximum power gain frequency) {f}-{\textsf {max}} beyond 300 MHz, are presented. Self-Alignment was used to realize TFTs with channel length down to 0.5 \mu \text{m}. The layout of these TFTs was optimized for good AC performance. Besides the channel dimensions, this includes ground-signal-ground contact pads. The AC performance of these short channel devices was evaluated by measuring their two port scattering parameters. These measurements were used to extract the unity gain power frequency from the maximum stable gain and the unilateral gain. The two complimentary definitions result in {f}-{\textsf {max}} values of (304 ± 12) and (398 ± 53) MHz, respectively. Furthermore, the transistor performance is not significantly altered by mechanical strain. Here, {f}-{\textsf {max}} reduces by 3.6% when a TFT is bent to a tensile radius of 3.5 mm.