Two key Samsung companies are merging in a step toward ensuring the son of the group's ailing chairman inherits control of the theme parks to smartphones conglomerate.

Samsung said on Tuesday that its de facto holding company Cheil Industries Inc will acquire Samsung C&T Corp by offering 0.35 new Cheil shares for every Samsung C&T share.

The move, to be completed by Sept 1, requires shareholder approval, which is expected. The combined entity will be named Samsung C&T.