This work investigates dynamic negative bias temperature instability (NBTI) in p-channel low-temperature polycrystalline silicon thin-film transistors (LTPS TFTs) with different rise and fall times. Experimental results reveal identical increases in the interface state density (Nit) induced by different dynamic NBTI stress conditions. Nevertheless, the degradation of the grain boundary trap (Ntrap) becomes more significant as rise time decreases to 1 μs. Because the surface inversion layer cannot form during the short rise time, transient bulk voltage will cause excess holes to diffuse into the poly-Si bulk. Therefore, the significant Ntrap increase is assisted by this transient effect.