AbstractFlexible, semitransparent and robust heating arrays have been designed by grayscale printing as ready‐to‐use devices for point‐of‐care application. A perforated Ag mesh is first fabricated with tunable features by controllably varying the toner grayscale value during laser printer on PET. The resistance could be varied between 1 to 2 Ω by tuning the Ag fill factor from 50 to 70 %. The Ag/PET heater based on joule heating is able to attain highly stable temperatures upto ∼135 °C maintained over long hours. Since temperature is directly related to resistance, this provides a fine temperature knob without any cumbersome processing steps. The merit of design allows individual heating elements to attain stable temperatures at low voltages (∼1.5 V) without any interference from neighboring heaters of the array, thus resulting in a thermal library. A laptop USB with 5.1 V output is able to power the thermal library for temperatures in the range of 30–60 °C, useful in many practical applications. It is a multipurpose disposable chip for in‐situ transmission microscopy that can be utilized for bioassay and point‐of‐care diagnostics, as demonstrated in the study.