Thanks to the great work of Nobuhiro Iwamatsu and others, Debian has an unofficial SH4 port which is close to complete (> 90% of the packages built).
In order to help developers to fix bugs on this architecture, I have produced an SH4 QEMU image which is available at the same location as my other QEMU images.
You will need a recent GIT HEAD QEMU to use it. Previous versions suffer from bugs in the MMU, causing segfaults and gratuitous TLB flushing. The MMU emulation is now hopefully correct, but still a bit slow. Also the emulated board is limited to 64 MB of memory, and this value can’t be changed as memory extension would overlap the addresses used for peripherals.
Update: I have backported the necessary SH4 patches into the QEMU Debian package version 0.12.3+dfsg-4.