1. A semiconductor device comprising a gallium arsenide substrate, a prediffused array of elementary gates provided on said substrate to form an integrated circuit designated as a "custom made circuit", wherein the elementary gates comprising the elements of the prediffused array form OR/NOR gates in accordance with source-coupled FET logic (SCFL) and comprise both internal gates for the "custom made circuit" and external gates compatible with ECL logic, the external gates directly connecting the circuit thus formed to an external semiconductor device realized in accordance with ECL logic, said external gates being constituted by two interconnected circuit blocks, a first block P.sub.I comprising an internal gate and a second block P.sub.E, the first block P.sub.I comprising a transistor T.sub.1 ' connected to a direct voltage supply V.sub.DD through a load R' controlled by a reference signal V.sub.REF and coupled by its source to a cascade of 1 to 6 transistors T.sub.1. .. T.sub.6, whose commonly-connected drains are connected to the voltage supply V.sub.DD through a load R, whose gates receive the control signals E.sub.1. .. E.sub.6, the commonly-connected sources of the transistors T.sub.1 ' and T.sub.1. .. T.sub.6 being supplied with current from a direct voltge -V.sub.SS on the one hand having the same absolute value as the voltage V.sub.DD and on the other hand such that: EQU -V.sub.SS &lt;V.sub.REF &lt;V.sub.DD, by means of a field effect transistor T.sub.2 and of a load R.sub.2 constituting a current source, and is then constituted by two buffer stages constituted by a follower transistor T.sub.3 and T.sub.3 ', respectively, connected to a transistor T.sub.4 and T.sub.4', respectively, connected as level translators, the drain of the follower transistor T.sub.3 or T.sub.3 ' being connected to the direct voltage supply V.sub.DD and the gate of the follower transistor T.sub.3 or T.sub.3 ' being controlled by the signal derived from the commonly-connected drain of the transistors T.sub.1. .. T.sub.6 and T.sub.1 ', the outputs Q.sub.I and Q.sub.I of the NOR and OR, respectively, being available at the source of the transistor T.sub.3 on the one hand and at the source of the transistor T.sub.3 ' on the other hand.