A new host material for Single‐Layer Phosphorescent Organic Light‐Emitting Diodes (SL‐PhOLED) is reported, namely SPA‐2‐FDMB, using the dimesitylborane (DMB) fragment as an acceptor unit. The molecular design is constructed on the general donor‐spiro‐acceptor architecture, which consists of connecting, via a spiro bridge, a donor and an acceptor units in order to avoid strong interaction between them. The DMB fragment is known for many electronic applications (notably Aggregation‐Induced Emission) but has not been used yet for SL‐PhOLED applications. This appears particularly interesting, as the development of this simplified technology has shown that only a few electron‐accepting fragments such as diphenylphosphine oxide can provide high‐performance devices. Herein, the yellow‐emitting SL‐PhOLED using SPA‐2‐FDMB as host presents an External Quantum Efficiency of 8.1% (Current Efficiency of 24.9 cd.A−1) with a low threshold voltage of 2.6 V. As SPA‐2‐FDMB presents a sharp HOMO/LUMO difference, the good matching of HOMO and LUMO energy levels with the Fermi level of the electrodes is responsible for these performances. The low LUMO level of −2.61 eV also appears particularly important. These performances are, to date, the highest reported for a yellow/orange‐emitting SL‐PhOLED and show the potential of DMB unit in the single‐layer technology.