Measurements of (i) the time-resolved photoluminescence and (ii) pressure dependence of the emitted light energy in two series of quaternary (AlInGa)N multiquantum wells have been used to point out the small magnitude of internal electric field as promoting highly efficient luminescence in these specially designed heterostructures. Findings of the experimental examination give the magnitude of built-in electric field few times smaller than that predicted theoretically. Electrical transport measurements support the explanation of the obtained results consisting of the screening of the built-in electric field by means of unintentional doping. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)