By Jonathan Stempel

(Reuters) - U.S. securities class actions have soared to a two-decade high, topping levels during the financial crisis, after a landmark January 2016 ruling meant to deter lawsuits in Delaware that accomplish nothing for shareholders sent many lawyers scurrying instead to federal courts.

There were 270 shareholder lawsuits in 2016 accusing companies of making false or misleading statements or concealing bad news about their businesses or mergers, a study released on Tuesday by Cornerstone Research and Stanford Law School shows.

The number rose from 188 in 2015, and was the highest since the Private Securities Litigation Reform Act, designed to curb frivolous lawsuits, took effect in 1995. A separate study last week from NERA Economic Consulting also noted a two-decade high.

Cornerstone attributed much of the increase to a surge in federal lawsuits challenging mergers, to 80 from 17.

That trend could prove sustainable.

It followed a series of Delaware state court decisions culminating in Chancellor Andre Bouchard's January 2016 rejection of a settlement arising from Zillow Group Inc's <ZG.O> purchase of online real estate rival Trulia Inc.

Chancery Court judges decided to no longer reflexively approve "disclosure-only" settlements requiring companies merely to reveal more, often immaterial details about their mergers.

Lawyers are not entitled to six- or seven-figure paydays for winning that, the judges said.

Roughly half of the Fortune 500 companies are incorporated in Delaware, long seen as having laws favorable to business.

Cornerstone said the number of traditional securities class actions, often following revelations of weak financial results or regulatory probes, rose to 189 last year from 170 in 2015.

It said the "maximum dollar loss," or largest sums that shareholders might claim in damages, rose to $823 billion from $371 billion, and topped even the $816 billion level from 2008.

Eighty of the 270 lawsuits targeted biotechnology, healthcare and pharmaceutical companies. Thirty-four targeted financial companies.

NERA, meanwhile, said settlements also increased, to 113 last year from 109 in 2015.

It said the average settlement was $72 million, topped by HSBC Holdings Plc's <HSBA.L> $1.575 billion accord over lending practices at Household International Inc, a consumer finance company it bought, and Merck & Co's <MRK.N> $1.06 billion accord over its marketing of the painkiller Vioxx.

Those settlements were long in coming. The Household litigation began in 2002, and the Merck litigation in 2005.

A $7.2 billion settlement in 2006 over energy company Enron Corp's collapse remains the largest on record.

(Reporting by Jonathan Stempel in New York; Editing by Frances Kerry)