ChIP-chip (or ChIP-on-chip) is a technology for isolation and identification of genomic sites occupied by specific DNA-binding proteins in living cells. The ChIP-chip signals can be obtained over the whole genome by tiling arrays, where a peak shape is generally observed around a protein-binding site. In this article, we describe the ChIP-chip process and present a probability model for ChIP-chip data. We then propose a model-based method for recognizing the peak shapes for the purpose of detecting protein-binding sites. We also investigate the issue of bandwidth in nonparametric kernel smoothing method.