Ultracompact simultaneous XOR and XNOR logic gates are proposed and analyzed. The suggested design is based on two-dimensional Si photonic crystal (PhC) with a central hole infiltrated by nematic liquid crystal (NLC) of type E7. The plane wave expansion method is used to obtain the photonic bandgap for both transverse electric mode and transverse magnetic mode. Further, the transmission through the proposed logic gates is calculated by the full vectorial finite element method. The numerical results show that the reported XOR and XNOR logic gates can be operated around wavelength of 1500 nm. In addition, the operation of the designed logic gates can be switched on/off by controlling the NLC biasing state. Such PhC logic gates have a compact size of 47  μm² and can achieve a large contrast ratio of 26 dB. Therefore, the suggested design has advantages in terms of tunability, low power consumption, compact size, simplicity, and compatibility with nowadays fabrication technology, which will be suitable for photonic integrated circuits.