<p>This paper explores the impact of spacer materials on the performance of a dual-material (DM) junctionless (JL) Tree-FET device, analyzing its direct current (DC) and analog/radio frequency (RF) characteristics. Single-κ (S-κ) spacers, including air, SiO₂, Si₃N₄, HfO₂, and TiO₂, as well as dual-κ (D-κ) combinations of air + HfO₂, SiO₂ + HfO₂, air + TiO₂, and SiO₂ + TiO₂ are evaluated herein. The study reveals significant improvements in DC performance with the TiO₂ spacer in the S-κ configuration, including an <i>I</i>_ON/<i>I</i>_OFF ratio, subthreshold slope (SS), and drain-induced barrier lowering (DIBL) of ~10¹⁰, 62.51&#xa0;mV/dec and 15.26&#xa0;mV/V, respectively. Analog/RF parameters such as transconductance (<i>g</i>_m), gain (A_v), transconductance generation factor (TGF), and gain–frequency product (GFP) also improve with TiO₂. The D-κ (air + TiO₂) spacer further enhances DC and analog/RF performance, while the D-κ (air + HfO₂) spacer excels in linearity due to reduced harmonic distortion. Additionally, a common-source amplifier using the D-κ (SiO₂ + TiO₂) spacer achieves a 67.24% higher gain compared to the S-κ (TiO₂) spacer. This research demonstrates the potential for optimized spacer materials in advancing the efficiency and performance of DM JL Tree-FET devices in modern semiconductor applications.</p>