Photonic crystal microcavities with multi-hole defects were simulated using finite difference time domain (FDTD) analysis. Subwavelength, multi-hole defects (MHD) offer a significant increase in defect surface area without compromising the quality factor of the photonic crystal. Calculations of the increase in surface area compared to a traditional, single hole defect are performed for MHD structures with varying subwavelength defect hole size, subwavelength defect hole spacing, and effective defect radius. For active photonic crystal applications, the resonance wavelength and quality factor of several different MHD photonic crystal structures was calculated as a function of the dielectric constant of the defect. MHD photonic crystals can be designed to enable large changes in resonance wavelength for small changes in defect dielectric constant. These structures would be advantageous for applications in biosensing and optical switching.© (2008) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.