  We present a photometric study of the stars in ionizing star clusters
embedded in several giant HII regions of M33 (CC93, IC 142, NGC 595, MA2, NGC
604 and NGC 588). Our photometry are based on the HST-WFPC2 images of these
clusters. Color-magnitude diagrams and color-color diagrams of these clusters
are obtained and are used for estimating the reddenings and ages of the
clusters. The luminosity functions (LFs) and initial mass functions (IMFs) of
the massive stars in these clusters are also derived. The slopes of the IMFs
range from Gamma = -0.5 to -2.1. It is found interestingly that the IMFs get
steeper with increasing galactocentric distance and with decreasing [O/H]
abundance.
