A previously reported ac magnetic‐field technique has here been applied to selective recrystallization on quartz substrates of polysilicon thin films which had been patterned into specific microblock designs. With the recrystallization it has been possible to produce single‐crystal silicon microblocks of a maximum size of approximately 60×40×2 &mgr;m,3large enough for the fabrication of high‐performance thin‐film transistors. Microblocks used in the experiments were of two types: ‘‘network’’ rectangles, connected on the wafer two dimensionally with polysilicon paths, and ‘‘isolated’’ rectangles adjacent to the network rectangles. The surface morphology of the recrystallized silicon films was observed with scanning electron microscopy. While no grain boundaries were found on the surfaces of the recrystallized network rectangles, many grain boundaries were observed to remain on the recrystallized isolated rectangles. X‐ray diffractions for the recrystallized network rectangles were measured with a microfocused x‐ray beam, and the recrystallized network rectangles were confirmed to be single‐crystal silicon microblocks of good crystal quality. It had been expected that network rectangles would be more greatly heated, as compared to isolated rectangles, by the eddy currents induced by the ac magnetic fields, and the observed higher quality of network‐rectangle recrystallization has verified that anticipated eddy‐current contribution.