  We discuss the influence of disorder on domain structure formation in
ferromagnetic phase of diluted magnetic semiconductors (DMS) of p-type. Using
analytical arguments we show the existence of critical ratio $\nu_{\rm {cr}}$
of concentration of charge carriers and magnetic ions such that sample critical
thickness $L_{\rm{cr}}$ (such that at $L<L_{\rm{cr}}$ a sample is monodomain)
diverges as $\nu \to \nu_{\rm {cr}}$. At $\nu > \nu_{\rm {cr}}$ the sample is
monodomain. This feature makes DMS different from conventional ordered magnets
as it gives a possibility to control the sample critical thickness and emerging
domain structure period by variation of $\nu $. As concentration of magnetic
impurities grows, $\nu_{\rm {cr}}\to \infty$ restoring conventional behavior of
ordered magnets. Above facts have been revealed by examination of the
temperature of transition to inhomogeneous magnetic state (stripe domain
structure) in a slab of finite thickness $L$ of p-type DMS. Our analysis is
carried out on the base of homogeneous exchange part of magnetic free energy of
DMS calculated by us earlier [\prb, {\bf 67}, 195203 (2003)].
