A submanifold generated by plane leaves of codimension two in a Euclidean space is, in general, intrinsically a Riemannian manifold of conullity two. All such manifolds have been classified into four classes: planar, hyperbolic, parabolic, and elliptic, i.e. having, respectively, infinitely many, two, one, or no real intrinsically asymptotic distributions. It is proved that if such a submanifold is semiparallel and intrinsically a manifold of conullity two, then it must be planar. This verifies, for the case considered here, a conjecture that a semiparallel submanifold, which is intrinsically of conullity two, must be planar. Validity of this conjecture has been established previously by the author for the three-dimensional semiparallel submanifolds.