1. Operating Temperature Range: This is the only substantive difference. BC858CW-HF: Only specifies a maximum junction temperature of 150°C, with no defined lower operating temperature limit. BC858CW-G: Explicitly rated for -65°C to 150°C (Tj). The BC858CW-G is a fully characterized wide-temperature device, with its performance guaranteed across the entire -65°C to 150°C range. This makes it suitable for industrial, automotive, or any demanding application that may encounter low-temperature environments. The datasheet parameters for the BC858CW-HF may be ambiguous at the low-temperature end (e.g., below 0°C). While it may physically be the same die, its low-temperature performance is not formally defined in the specification. Using it in a rigorous design or in applications requiring specific certifications (e.g., AEC-Q) carries inherent risk. Direct substitution with the G variant eliminates this uncertainty.