Silicone pressure-sensitive adhesives (Si-PSA) are relatively new materials used in the adhesive industry. The first Si-PSA adhesives used in industry were presented in the 1960s. Still, only in the last two decades, has this type of adhesive increased its importance due to new possible applications, such as medical plasters and assembly tapes. Silicone self-adhesive materials found applications in adhesive joints operating at extreme temperatures, even in the range of –70 °C ÷ 300 °C. The self-adhesive and mechanical properties of silicone pressure-sensitive adhesives depend largely on the type and concentration of the cross-linking compound. Most often, organic peroxides are mainly used, such as benzoyl peroxide (BPO) or dichlorobenzoyl peroxide (DClBPO) at temperatures from 120 to 150 °C. To increase resistance and thermal stability, small amounts of silicon fillers as diatomite are added to commercial peroxide-crosslinked polydimethylsiloxane resins. The influence of different diatomite concentrations on the self-adhesive properties of silicone pressure-sensitive adhesives was studied and presented in this work. The most important application properties were tested: peel adhesion, tack, cohesion at room and elevated temperature, SAFT test (Shear Adhesive Failure Temperature), pot life (viscosity), and shrinkage. The obtained results were compared with those of the unmodified tapes. During the studies, a significant increase in thermal resistance and decreased shrinkage were achieved for newly obtained silicone pressure-sensitive tapes. Peel adhesion, shear strength and tack of prepared samples have acceptable levels for industrial purposes. Even small amounts of diatomite filler (up to 3pph) significantly improve the performance of silicone self-adhesive adhesives, especially when used in unfavorable conditions of high temperatures.