A silane containing a bulky hydrocarbon group or groups R therein and having the formula (III) R.sub.3-(x+y)(R.sup.1).sub.x(R.sup.2).sub.ySi(OR.sup.3) can be produced by reacting a silane of the formula (I) (R.sup.1).sub.x(R.sup.2).sub.ySiCl.sub.3-(x+y)(OR.sup.3) with a Grignard reagent of the formula (II) RMgX Further, a tri-organo-chlorosilane of the formula (XIIa) (R.sup.1)(R.sup.2)(R.sup.3)SiCl can be produced by reacting a tri-organo-silane of the formula (XIa) (R.sup.1)(R.sup.2)(R.sup.3)SiZ.sup.1 with hydrochloric acid.Furthermore, a tri-organo-monoalkoxysilane of the formula (XXIII) R.sub.3-(x+y)(R.sup.1).sub.x(R.sup.2).sub.ySi(OR.sup.3) can be produced when a silane of the formula (XXI) (R.sup.1).sub.x(R.sup.2).sub.ySiCl.sub.4-(x+y) is reacted with a Grignard reagent of the formula (XXII) RMgX with addition of and reaction with an alcohol or an epoxy compound during the reaction.