This paper presents two miniature fully-integrated CMOS-compatible laterally diffused metal oxide semiconductor (LDMOS) power amplifiers (PAs) in 40-nm CMOS process. Due to the high breakdown voltage characteristic, LDMOS provides superior power density than modern standard CMOS transistor. The capacitive neutralization technique is adopted to improve stability of LDMOS transistor while enhancing the maximum available gain. For low-cost miniaturization, the transformers are utilized in the proposed PAs. Also, efficient power combining and impedance transformation can be realized. The LDMOS PAs achieve saturated output power (Psat) of 26.7 and 26.5 dBm and measured OP1dB of 24.24 and 24.1 dBm at 2.5 and 3.5 GHz, respectively. With compact chip size of 0.318 mm2 and 0.259 mm2, two PAs demonstrate the highest Psat power area density (PAD) of 1467 mW/mm2 and 1724 mW/mm2 at 2.5 and 3.5 GHz among recently reported CMOS PAs.