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We imaged circumstellar disks around 22 Herbig Ae/Be stars at 25 \mu m usingSubaru/COMICS and Gemini/T-ReCS. Our sample consists of equal numbers ofobjects belonging to the two categories defined by Meeus et al. (2001); 11group I (flaring disk) and II (at disk) sources. We find that group I sourcestend to show more extended emission than group II sources. Previous studieshave shown that the continuous disk is hard to be resolved with 8 meter classtelescopes in Q-band due to the strong emission from the unresolved innermostregion of the disk. It indicates that the resolved Q-band sources require ahole or gap in the disk material distribution to suppress the contribution fromthe innermost region of the disk. As many group I sources are resolved at 25\mu m, we suggest that many, not all, group I Herbig Ae/Be disks have a hole orgap and are (pre-)transitional disks. On the other hand, the unresolved natureof many group II sources at 25 \mu m supports that group II disks havecontinuous at disk geometry. It has been inferred that group I disks may evolveinto group II through settling of dust grains to the mid-plane of theproto-planetary disk. However, considering growing evidence for the presence ofa hole or gaps in the disk of group I sources, such an evolutionary scenario isunlikely. The difference between groups I and II may reflect differentevolutionary pathways of protoplanetary disks.

High-resolution 25 \mu m imaging of the disks around Herbig Ae/Be stars