Solution to an isotopism question conerning rank 2 semifields

In [8] Dempwolff gives a construction of three classes of rank two semifields of order $q^2n$, with $q$ and $n$ odd, using Dembowski–Ostrom polynomials. The question whether these semifields are new, i.e. not isotopic to previous constructions, is left as an open problem. In this paper we solve this problem for $n > 3$, in particular we prove that two of these classes, labeled D A and D A B, are new for $n > 3$, whereas presemifields in family D B are isotopic to Generalized Twisted Fields for each $n ≥ 3$.