Heavy squark decays into top and charginos or neutralinos could be an unexpected source of top quarks at hadron colliders. A detailed treatment of these processes is necessary for a reliable calculation of both the top quark production cross-section and the standard top quark branching ratio in the MSSM. Along this line we compute the electroweak corrections to the sbottom decays b̃a → χ-i t within the Yukawa coupling approximation. The calculation of these higher order contributions requires renormalization of both the bottom squark mixing angle and of tanβ. This type of corrections gives the leading order electroweak effects at low and high tanβ. © 1998 Elsevier Science B.V. All rights reserved.