A novel spiro-type material (5H,5′H-10,10′-spirobi[dibenzo[b,e][1,4]azasiline]-5,5′-diyl)bis((4-methoxyphenyl)-methanone) (SDBSO) was designed and synthesized. The introduction of spirobi[dibenzo[b,e][1,4]azasiline] causes the material to retain high triplet energy (over 3.10 eV). In addition, owing to its highly steric and rigid structure and spiro-linkage, SDBSO exhibited good thermal stability and suitable frontier molecular orbital (FMO) energy levels. The RGB (blue, green, and red) three-color phosphorescent organic light-emitting diodes with SDBSO as the host material were fabricated and maximum external quantum efficiencies of over 20% were achieved for the green and red devices with relatively flat roll-off, indicating its potential utility as a host-building block for highly efficient PHOLEDs.