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Propagation delay times of high-speed VLSI candidates ISL and STL are calculated analytically. It is shown by calculations and measurements that STL is marginally faster than ISL in oxide-isolated processes, at the cost of higher process complexity. Both logic forms suffer from speed degradation due to fan-in. Measures to obtain delay times that are independent of fan-in are discussed. Fan-out aspects are also considered. It is shown that ring oscillators exhibit a somewhat better speed than logic gates that start to switch from the DC state. This speed difference is expressed in an empirical formula.