We demonstrate a near-infrared (NIR) photodiode (PD) by using a wave-shaped sidewall silicon nanopillars (WS-SiNPs) structure. The designed WS sidewall nanostructure increases the horizontal component of incident light and induces multiple whispering-gallery modes with low-quality factor, which increases the light absorption path. Thus, the WS-SiNP PD shows improved spectral responsivity and external quantum efficiency over straight sidewall silicon nanopillars and planar PDs in the NIR region. Especially, the peak responsivity of 0.648 A/W is achieved at a wavelength of 905 nm, which is used for light detection and ranging. Comparison with commercial photodiodes demonstrates the good optoelectrical characteristics of the fabricated device. The improved characteristics are validated by 3D finite differential time domain simulations. Based on these results, our device shows the potential for cost-effective Si-based optoelectronic devices to be utilized in future advanced applications.